Quartz glass crucible and method for manufacturing the quartz glass crucible

Abstract

To provide a quartz glass crucible capable of suppressing the contamination of metal impurities occurring in a silicon melt from the outer surface of the quartz glass crucible to suppress the abnormality of a silicon single crystal due to the impurities, and a method for manufacturing the same.SOLUTION: Each content of metal elements included on the outer surface of a quartz glass crucible is less than 0.5 ppm; the surface roughness Ra of the outer surface is 8 μm or more and 15 μm or less; and a porosity in a depth of 1 mm from the outer surface is 20% or more and 30% or less. The quartz glass crucible is manufactured by passing the step of molding and melting quartz powder to form a quartz glass crucible and reacting the outer surface of the quartz glass crucible with reactive gas mainly having chlorine based gas.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a quartz glass crucible for containing a polysilicon melt as a raw material and a method for manufacturing the quartz glass crucible, which are used when pulling up a silicon single crystal by the Chochralski method (hereinafter referred to as the CZ method).

Background Art

[0002] In the production of silicon single crystals, the CZ method is widely used. In this method, a seed crystal is brought into contact with the surface of a polysilicon melt as a raw material contained in a quartz glass crucible, the quartz glass crucible is rotated, and the seed crystal is rotated in the opposite direction and pulled upward to grow a single crystal ingot at the lower end of the seed crystal. In the above method, a quartz glass crucible for containing a polysilicon melt generally uses a quartz glass crucible whose inner layer is made of transparent silica glass and whose outer layer is made of opaque silica glass containing a large number of bubbles.

[0003] When this quartz glass crucible is used, cristobalite is generated due to impurities and minute irregularities on the inner surface of the quartz glass crucible. Therefore, before containing polysilicon in the quartz glass crucible, the inner surface of the quartz glass crucible is washed to remove impurities and minute irregularities on the inner surface.

[0004] Specifically, when the quartz glass crucible contains polysilicon and is heated to a temperature equal to or higher than the melting point of silicon (about 1400 ° C), usually, a brown ring-shaped cristobalite, so-called brown mold (also referred to as brown ring or brown mark), is generated on the inner surface of the crucible due to the crystallization of silica glass. This brown mold is formed by the crystal nuclei of the generated cristobalite gradually growing and expanding by heating, causing roughness and peeling on the inner surface of the crucible, and chips peeled off into the polysilicon melt are mixed in, resulting in dislocations in the silicon single crystal. Therefore, in order to remove the starting point for cristobalite nucleation, the inner surface of the quartz glass crucible is cleaned before the polysilicon is placed inside.

[0005] As a cleaning treatment for the inner surface of the crucible, for example, Patent Document 1 proposes a cleaning treatment in which the inner surface of a quartz glass crucible is sequentially cleaned with pure water, cleaned with a surfactant, cleaned with a 0.2 to 1% by weight aqueous solution of hydrofluoric acid, and cleaned with pure water. This cleaning method suppresses the generation of minute irregularities on the inner surface of the crucible during cleaning, and also allows for the efficient removal of dust and impurities. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-17241 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, in a silicon single crystal pulling apparatus, the quartz glass crucible is held by a carbon crucible, which has a larger diameter than the quartz glass crucible, and is heated by a heater placed around it. Then, after the polysilicon in the quartz glass crucible is melted by the heat from this heater, a seed crystal is brought into contact with the surface of the molten polysilicon, thereby pulling up the silicon single crystal.

[0008] During this process, the thermal reaction between the heated quartz glass crucible and the carbon crucible causes metallic impurities such as Fe, Cr, Ni, and Cu, which were present near the outer surface of the quartz glass crucible, to diffuse into the crucible's interior and into the atmosphere. These diffused metallic impurities may then be incorporated into the silicon single crystal being pulled, potentially causing dislocations in the silicon single crystal.

[0009] In particular, the outer surface of a quartz glass crucible has a higher probability of contact with various sources of contamination at each stage of the manufacturing process compared to the inner surface. Furthermore, the outer surface of a quartz glass crucible has a greater surface roughness than the inner surface, and voids are formed near the outer surface. Therefore, the outer surface of a quartz glass crucible and its vicinity are more susceptible to metal impurities penetrating its roughness and voids, resulting in a higher level of metal impurity contamination than the inner surface. Furthermore, these metallic impurities on the outer surface may diffuse into the quartz glass crucible wall and the atmosphere, potentially leading to contamination originating from the outer surface of the quartz glass crucible and causing the single-crystal silicon to fail to meet quality requirements.

[0010] The present invention was made to solve the above technical problems, and provides a quartz glass crucible and a method for manufacturing the quartz glass crucible that suppress contamination by metal impurities from the outer surface of the quartz glass crucible generated during silicon melting, and suppress abnormalities such as dislocations caused by impurities in the silicon single crystal. [Means for solving the problem]

[0011] The quartz glass crucible according to the present invention is a quartz glass crucible for pulling silicon single crystals, characterized in that the content of each metal element contained in the outer surface of the quartz glass crucible is less than 0.5 ppm, the surface roughness Ra of the outer surface is 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface is 20% or more and 30% or less.

[0012] Thus, since the content of each metal element on the outer surface of the quartz glass crucible is less than 0.5 ppm, contamination of the quartz glass crucible with metal impurities from the outer surface can be suppressed, and abnormalities such as dislocations in the silicon single crystal caused by these metal impurities can be suppressed.

[0013] Furthermore, since the surface roughness Ra of the outer surface of the quartz glass crucible is 8 μm to 15 μm, and the void ratio at a depth of 1 mm from the outer surface is 20% to 30%, the quartz glass crucible and the carbon crucible adhere properly during silicon melting. Because the surface roughness Ra is between 8 μm and 15 μm, reaction gases do not accumulate between the quartz glass crucible and the carbon crucible, and instead pass through the space between them, thereby suppressing abnormal deformation of the quartz glass crucible. Furthermore, because the surface roughness Ra is between 8 μm and 15 μm, the peeling of unmelted quartz powder on the outer surface can be suppressed. For example, when removing a packaged quartz glass crucible from the packaging bag, it is possible to suppress the quartz powder that peels off from the outer surface of the quartz glass crucible from entering the inner surface of the quartz glass crucible.

[0014] Furthermore, because the porosity is between 20% and 30%, a minute space is created between the quartz glass crucible and the carbon crucible. This allows for smooth diffusion of heat heated by the heater, preventing localized heating and suppressing abnormal deformation of the quartz glass crucible.

[0015] Furthermore, the present invention was made to solve the above problems, and the method for manufacturing a quartz glass crucible according to the present invention is a method for manufacturing a quartz glass crucible for pulling silicon single crystals, characterized in that it includes a step of molding and melting quartz powder to form a quartz glass crucible, and then reacting the outer surface of the quartz glass crucible with a reactive gas mainly composed of chlorine.

[0016] In this way, by reacting the outer surface of the quartz glass crucible with a reactive gas mainly composed of chlorine, metal impurities on the outer surface of the quartz glass crucible are precipitated as metal salts, and the content of each metal element on the outer surface of the quartz glass crucible can be reduced to less than 0.5 ppm. Furthermore, as the chlorine-based reactive gas, gases such as Cl2 and HCl can be used.

[0017] Here, it is desirable that the step of reacting the outer surface of the quartz glass crucible with a reactive gas mainly composed of chlorine is carried out in a temperature range of 1000°C or higher and 1300°C or lower. Further, after the step of reacting the outer surface of the quartz glass crucible with a reactive gas mainly composed of chlorine, it is desirable that a step of etching the outer surface of the quartz glass crucible with an acid mainly composed of hydrofluoric acid is carried out. By adjusting the melting conditions of the quartz glass crucible or (and) by carrying out etching with an acid mainly composed of hydrofluoric acid, the surface roughness Ra of the outer surface of the quartz glass crucible can be set to 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface can be set to 20% or more and 30% or less.

Advantages of the Invention

[0018] According to the quartz glass crucible of the present invention, it is possible to obtain a quartz glass crucible and a method for manufacturing the same, which suppress contamination of metal impurities from the outer surface of the quartz glass crucible generated during silicon melting and suppress abnormalities such as dislocations caused by impurities in the silicon single crystal.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a reaction processing furnace for manufacturing a quartz glass crucible according to the present invention.

Embodiments for Carrying Out the Invention

[0020] Embodiments of the quartz glass crucible and the method for manufacturing the same according to the present invention will be described. The quartz glass crucible according to the present invention is a quartz glass crucible for pulling a silicon single crystal, wherein the content of each metal element contained in the outer surface of the quartz glass crucible is less than 0.5 ppm, the surface roughness Ra of the outer surface is 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface is 20% or more and 30% or less.

[0021] Thus, the metallic element content on the outer surface of the quartz glass crucible is less than 0.5 ppm for each metallic element. This suppresses contamination by metallic impurity elements from the outer surface of the quartz glass crucible during silicon melting, and suppresses abnormalities such as dislocations caused by impurities in the silicon single crystal. Furthermore, these metallic elements, which affect the quality of silicon single crystals, include Fe, Cr, Ni, and Cu. Other metallic elements include Mg, Ti, and V, but their content is inherently low, less than 0.5 ppm. Therefore, the present invention focuses on reducing the content of Fe, Cr, Ni, and Cu, which affect the quality of silicon single crystals. Then, by reacting a reactive gas, mainly chlorine-based gas, with the outer surface of a quartz glass crucible, metal impurities are precipitated as metal salts and removed, thereby reducing the amount of metal impurities present.

[0022] The surface roughness Ra of the outer surface of the quartz glass crucible is 8 μm to 15 μm, and the porosity at a depth of 1 mm from the outer surface is 20% to 30%. By adjusting the melting conditions of the quartz glass crucible, the surface roughness Ra of the outer surface of the quartz glass crucible can be set to 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface can be set to 20% or more and 30% or less. Furthermore, by reacting a reactive gas, mainly chlorine-based gas, with the outer surface of a quartz glass crucible, metal impurities are precipitated as metal salts. Then, the outer surface of the quartz glass crucible is etched with an acid, for example, mainly hydrofluoric acid, to achieve the surface roughness and porosity described above.

[0023] Here, we will explain the voids that form on the outer surface. In the manufacturing process of quartz glass crucibles, when quartz powder is melted by arc discharge, the quartz powder gradually melts from the innermost layer, with the outermost layer melting last. At this time, some quartz powder does not completely melt on the outer surface of the quartz glass crucible and remains as unmelted powder on the outer surface of the crucible. In this state, unmelted powder may fall off, and gaps (microcracks) may form on the outer surface of the crucible.

[0024] The reason for considering a void depth of 1 mm from the outer surface is that voids occur only in the very surface layer of the outermost surface, and most voids exist within a depth of 1 mm from the outer surface. Therefore, it is sufficient to examine the void ratio within a depth of 1 mm from the outer surface. The porosity is measured using the gas displacement method. Specifically, a sample and a comparison sample of the same volume are simultaneously subjected to gas release in a gas chamber, trapping the gas in the voids. The porosity (apparent density) can then be measured by the change in atmospheric pressure between the sample and the comparison sample of the same volume.

[0025] Furthermore, as described above, the surface roughness Ra of the outer surface of the quartz glass crucible is 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface is 20% or more and 30% or less. Here, if Ra is less than 8 μm and porosity is less than 20%, the adhesion between the quartz glass crucible and the carbon crucible during silicon melting becomes too high, and reaction gases from high-temperature contact between the two accumulate between the outer surface of the quartz glass crucible and the inner surface of the carbon crucible. This reaction gas may cause abnormal deformation of the quartz glass crucible, which is undesirable.

[0026] Furthermore, if Ra exceeds 15 μm and the porosity exceeds 30%, there is a risk that unmelted quartz powder adhering to the outer surface may peel off. For example, when removing a quartz glass crucible from its packaging bag, there is a risk that quartz powder peeled off the outer surface of the crucible may enter the inner surface of the crucible, which is undesirable.

[0027] Therefore, it is preferable that the surface roughness Ra of the outer surface of the quartz glass crucible is 8 μm or more and 15 μm or less, and the void ratio at a depth of 1 mm from the outer surface is 20% or more and 30% or less. This ensures proper contact between the outer surface of the quartz glass crucible and the inner surface of the carbon crucible during silicon melting, thereby suppressing deformation of the quartz glass crucible. Furthermore, the peeling of unmelted quartz powder on the outer surface can be suppressed. For example, when removing a quartz glass crucible packaged in a packaging bag from the bag, it is possible to suppress the quartz powder that peels off the outer surface of the quartz glass crucible from entering the inner surface of the crucible.

[0028] Furthermore, the quartz glass crucible according to the present invention can be applied to multilayer quartz glass crucibles, such as a two-layer structure or a three-layer structure, where the outer layer is a natural quartz glass layer and the inner layer is a synthetic quartz glass layer. The aforementioned natural quartz glass layer is an opaque layer with excellent heat resistance, although its purity is low, while the aforementioned synthetic quartz glass layer may be a transparent layer formed from a high-purity synthetic silica raw material obtained by hydrolysis of silicon alkoxide or the like.

[0029] Next, an embodiment of the method for producing a quartz glass crucible according to the present invention will be described. The method for producing a quartz glass crucible according to the present invention is the same as a general method for producing a quartz glass crucible up to the step of molding and melting quartz powder to form a quartz glass crucible. For example, let's consider a quartz glass crucible with a two-layer structure, where the outer layer is made of natural quartz glass and the inner layer is made of synthetic quartz glass. In this example, natural silica raw material powder to form the outer layer is loaded into a rotating crucible molding mold to a predetermined thickness, and synthetic silica raw material powder to form the inner layer is loaded inside to a predetermined thickness, and then the crucible is molded.

[0030] Subsequently, an arc electrode is inserted into this, and vitrification is performed by reduced-pressure arc melting to form the quartz glass crucible according to the present invention. Furthermore, in the manufacturing method of quartz glass crucibles, for example, by adjusting the etching time and chemical flow rate during the etching treatment with hydrofluoric acid aqueous solution, the surface roughness Ra of the outer surface of the quartz glass crucible can be set to 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface can be set to 20% or more and 30% or less. Alternatively, the inner layer may be formed by directly depositing it using a flame melting method after the outer layer has been formed.

[0031] The method for manufacturing a quartz glass crucible according to the present invention is not particularly limited up to the step of forming the quartz glass crucible, but is characterized by the subsequent step of removing metal impurities from the outer surface of the quartz glass crucible. As mentioned above, this quartz glass crucible is obtained by molding and melting SiO2 powder at high temperatures. Typically, the outer surface of the molten quartz glass crucible has fine voids (microcracks) due to the influence of raw material powder that did not completely melt during the process.

[0032] In the process of removing metal impurities from the outer surface of a quartz glass crucible, the outer surface of the quartz glass crucible is the unprocessed surface of the quartz glass crucible after the quartz powder has been molded and melted to form the quartz glass crucible. In this process of removing metal impurities, a quartz glass crucible is reacted with a reactive gas, mainly chlorine-based gas, at a high temperature of 1000-1300°C at a flow rate of 10 liters / min to 30 liters / min for 1 to 2 hours to accelerate the reaction. Furthermore, as the chlorine-based reactive gas, gases such as Cl2 and HCl can be used.

[0033] Specifically, the process of removing metallic impurities from the outer surface of a quartz glass crucible will be explained based on Figure 1. Figure 1 is a cross-sectional view showing the schematic configuration of a reaction furnace for manufacturing a quartz glass crucible according to the present invention. In Figure 1, reference numeral 1 denotes a reaction furnace, which is equipped with a heater 2. An inlet 3 for introducing a chlorine-based reactive gas G is provided at the bottom of the reaction furnace 1. An outlet 4 for discharging the chlorine-based reactive gas G is provided at the top of the reaction furnace 1. As shown in Figure 1, the quartz glass crucible R is placed face down on the base 5 of the reaction furnace 1, and the chlorine-based reactive gas G is brought into contact with the outer surface of the quartz glass crucible R.

[0034] Then, by reacting the mixture at a high temperature of 1000-1300°C with a flow rate of 10 liters / min to 30 liters / min for 1 to 2 hours, metal impurities present on the outer surface of the quartz glass crucible, originating from the manufacturing process, are precipitated as metal salts. Subsequently, metal impurities such as Fe, Cr, Ni, and Cu on the outer surface are reduced to 0.5 ppm or less by etching with an acid, primarily hydrofluoric acid (or by cleaning).

[0035] At this time, if the flow rate of the reactive gas is less than 10 liters / min, the probability of reaction with the quartz glass crucible decreases, which may reduce the effectiveness of reducing metal impurities, and is therefore undesirable. Furthermore, if the reactive gas flow rate exceeds 30 liters / min, the reaction efficiency may decrease because a reaction occurs due to the new gas before it has fully reacted with the outer surface of the quartz glass crucible, which is undesirable.

[0036] Furthermore, when reacting a reactive gas, mainly chlorine-based gas, with the outer surface of a quartz glass crucible, the reaction with the reactive gas will not proceed easily if the reaction field temperature is below 1000°C, and if it exceeds 1300°C, there is a risk of the crucible deforming. Furthermore, if the reaction time is less than one hour, the reaction between the reactive gas and metal impurities may not proceed sufficiently, potentially resulting in a reduced metal impurity removal effect. Also, if the reaction time exceeds two hours, no further improvement in reducing metal impurities can be expected, potentially leading to increased costs due to the wasteful use of reactive gas.

[0037] Next, a cleaning process is performed to remove the precipitated metal salt by cleaning (etching) the outer surface of the quartz glass crucible. In this cleaning process, the outer surface of the quartz glass crucible is etched with acid to remove precipitated metal salts, reduce metal impurities to 0.5 ppm or less, and achieve a predetermined surface roughness. This cleaning method is not particularly limited, and for example, the cleaning method described in Patent Document 1 may be used. Therefore, this cleaning process is also called an etching process.

[0038] This cleaning process is primarily performed to remove metal impurities deposited on the outer surface of the crucible. Preferably, the cleaning conditions are an aqueous hydrofluoric acid solution with a hydrofluoric acid concentration of 15-30% by weight, at a temperature of 35-45°C, a flow rate of 10-20 liters / min, and a chemical cleaning time of 10-20 minutes. By performing hydrofluoric acid cleaning under these conditions, metal impurities can be efficiently removed while suppressing the occurrence of minute irregularities on the outer surface of the crucible due to excessive etching (excessive increase in porosity).

[0039] Finally, a final rinse is performed using pure water. In this rinsing step, the hydrofluoric acid cleaning solution is completely removed. The specific cleaning conditions for this pure water rinsing can be the same as those for conventional pure water rinsing (as shown in Patent Document 1).

[0040] The quartz glass crucibles, cleaned through the process described above, are dried and then used for pulling silicon single crystals. The drying method is not particularly limited. A preferred drying method is, for example, to spray high-purity nitrogen gas at 30-50°C at a rate of 50-70 liters / min onto the outer surface of the crucible for 10-20 minutes.

[0041] In this way, by reacting a quartz glass crucible with a reactive gas mainly composed of chlorine gas at a high temperature of 1000 to 1300°C at a flow rate of 10 liters / min to 30 liters / min for 1 to 2 hours, and then performing acid etching cleaning, it is possible to manufacture a quartz glass crucible in which the metal element content on the outer surface of the quartz glass crucible is less than 0.5 ppm each, the surface roughness Ra of the outer surface is between 8 μm and 15 μm, and the porosity at a depth of 1 mm from the outer surface is between 20% and 30%.

[0042] The quartz glass crucible of the present invention suppresses the generation of metal impurities caused by the reaction between the quartz glass crucible and the carbon crucible due to the heat generated during silicon single crystal fabrication, making them less likely to be incorporated into the silicon single crystal. This enables the pulling of higher-purity silicon single crystals. [Examples]

[0043] (Example 1) A quartz glass crucible with an outer diameter of 32 inches and a height of 450 mm was fabricated using the rotary molding method and the arc melting method. The crucible's inner layer consisted of a 2 mm thick synthetic quartz glass layer, and the outer layer consisted of a 14 mm thick natural quartz glass layer. The metallic impurities contained in this raw material, natural quartz glass powder, were Fe, Cr, Ni, Cu, Mg, and V. The content of these metallic impurities was 1.5 ppm for Fe, 1.0 ppm for Cr, 1.0 ppm for Ni, 1.2 ppm for Cu, 0.05 ppm for Mg, and 0.01 ppm for V. Furthermore, the arc melting was performed at approximately 2000°C for less than one hour. Subsequently, using the reaction furnace shown in Figure 1, chlorine gas was reacted with the outer surface of a quartz glass crucible at 1200°C at a flow rate of 20 liters / min for 1 hour, as shown in Table 1.

[0044] The treated quartz glass crucibles were then washed (etched) with a 15% by weight hydrofluoric acid aqueous solution at a temperature of 40°C, a flow rate of 15 liters / min, and a washing time of 15 minutes, as shown in Table 1. After that, they were rinsed with pure water as a final rinse and dried.

[0045] Subsequently, the surface roughness and porosity of the outer surface of the quartz glass crucible were measured. Further chemical analysis by acid dissolution was then performed to investigate the amount of metal impurities Fe, Cr, Ni, and Cu. First, the surface roughness of the outer surface was measured using a contact-type surface roughness measuring instrument (JIS B 0633:2001). Furthermore, the porosity was measured using the gas displacement method. Specifically, the sample and a comparison sample of the same volume were simultaneously subjected to gas release in a gas chamber, trapping the gas in the voids. The porosity (apparent density) was then measured by the change in atmospheric pressure between the sample and the comparison sample of the same volume.

[0046] The amount of the aforementioned metal impurities was measured by a chemical analysis method using acid dissolution. Specifically, a specified amount of 25% by weight hydrofluoric acid was reacted in a quartz glass crucible for 20 minutes, the resulting solution was collected, and the amount of impurities in the solution was measured by chemical analysis using an ICP-MS instrument. Furthermore, metal impurities other than Fe, Cr, Ni, and Cu were excluded from consideration because their amounts were trace.

[0047] As a result, the surface roughness Ra of the outer surface was 11 μm and the porosity was 25%. The amounts of metal impurities were 0.3 ppm for Fe, 0.2 ppm for Cr, 0.2 ppm for Ni, and 0.2 ppm for Cu. The results are shown in Table 2.

[0048] Furthermore, the deformation of quartz glass crucibles was investigated. The deformation was examined by placing the quartz glass crucibles inside an open furnace and heating them to 1200°C using a reactive gas and heater. The results are shown in Table 2. Furthermore, we investigated whether any unmelted quartz glass powder had fallen off the outer surface of the quartz glass crucibles. To investigate for powder fallout, we prepared a transparent bag made of PE or similar material, packed the quartz glass crucible in it, subjected it to some impact, removed the crucible from the bag, and checked whether any powder had fallen into the bag. The results are shown in Table 2.

[0049] Furthermore, this quartz glass crucible was used to pull silicon single crystals, and the presence or absence of deformation in the silica glass crucible after use was investigated. The pulling conditions for the silicon single crystal were 1300-1500°C for 50 hours. Deformation was investigated by examining the condition of the quartz glass crucible after use to determine if deformation was present. The results are shown in Table 2.

[0050] (Example 2) A quartz glass crucible was manufactured using the same method as in Example 1. Subsequently, as shown in Table 1, a cleaning process (etching process) was performed using a hydrofluoric acid aqueous solution with a hydrofluoric acid concentration of 15% by weight, at a temperature of 40°C, a flow rate of 10 liters / min, and a cleaning time of 10 minutes. Other conditions were the same as in Example 1, and various measurements and the presence or absence of deformation were performed. The results are shown in Table 2.

[0051] (Example 3) A quartz glass crucible was manufactured using the same method as in Example 1. Subsequently, as shown in Table 1, a cleaning process (etching process) was performed using a hydrofluoric acid aqueous solution with a concentration of 15% by weight, at a temperature of 40°C, a flow rate of 20 liters / min, and a cleaning time of 15 minutes. Other conditions were the same as in Example 1, and various measurements and the presence or absence of deformation were performed. The results are shown in Table 2.

[0052] (Comparative Example 1) As shown in Table 1, quartz glass crucibles were manufactured under the same conditions as in Example 1, except that chlorine gas was reacted with the outer surface of the quartz glass crucible at 1200°C at a flow rate of 5 liters / min for 1 hour. Subsequently, the roughness of the outer surface and the porosity were measured. As a result, the surface roughness Ra of the outer surface was 12 μm and the porosity was 28%. Furthermore, the amount of metal impurities was investigated in the same manner as in Example 1. The amounts of metal impurities were 0.8 ppm for Fe, 0.6 ppm for Cr, 0.5 ppm for Ni, and 0.5 ppm for Cu. The results are shown in Table 2.

[0053] Furthermore, similar to Example 1, we investigated the deformation of the quartz glass crucible, the shedding of powder, and whether the quartz glass crucible was deformed after use. The results are shown in Table 2.

[0054] (Comparative Example 2) As shown in Table 1, quartz glass crucibles were manufactured under the same conditions as in Example 1, except that chlorine gas was reacted with the outer surface of the quartz glass crucible at 1500°C at a flow rate of 15 liters / min for 2 hours, and a hydrofluoric acid aqueous solution with a concentration of 15% by weight was used at a temperature of 40°C, a flow rate of 15 liters / min, and a washing time of 3 minutes. The roughness of the outer surface and the porosity were measured under the same conditions as in Example 1. As a result, the surface roughness Ra of the outer surface was 3 μm and the porosity was 8%. Furthermore, the amount of metal impurities was investigated in the same manner as in Example 1. The amounts of metal impurities were 0.4 ppm for Fe, 0.3 ppm for Cr, 0.4 ppm for Ni, and 0.3 ppm for Cu. The results are shown in Table 2.

[0055] Furthermore, similar to Example 1, we investigated the deformation of the quartz glass crucible, the shedding of powder, and whether the quartz glass crucible was deformed after use. The results are shown in Table 2.

[0056] (Comparative Example 3) As shown in Table 1, quartz glass crucibles were manufactured under the same conditions as in Example 1, except that the outer surface of the quartz glass crucible was reacted with chlorine gas at 1000°C at a flow rate of 10 liters / min for 0.5 hours, and a 15% by weight hydrofluoric acid aqueous solution was used at a temperature of 40°C, a flow rate of 15 liters / min, and a washing time of 30 minutes. The roughness of the outer surface and the porosity were then measured. As a result, the surface roughness Ra of the outer surface was 20 μm and the porosity was 40%. Furthermore, the amount of metal impurities was investigated in the same manner as in Example 1. The amounts of metal impurities were 0.1 ppm for Fe, 0.1 ppm for Cr, 0.1 ppm for Ni, and 0.1 ppm for Cu. The results are shown in Table 2. Furthermore, similar to Example 1, we investigated the deformation of the quartz glass crucible, the shedding of powder, and whether the quartz glass crucible was deformed after use. The results are shown in Table 2.

[0057] (Comparative Example 4) As shown in Table 1, quartz glass crucibles were manufactured under the same conditions as in Example 1, except that the outer surface of the quartz glass crucible was reacted with chlorine gas at 800°C at a flow rate of 10 liters / min for 2 hours, and a 15% by weight hydrofluoric acid aqueous solution was used at a temperature of 40°C, a flow rate of 15 liters / min, and a washing time of 25 minutes. The roughness of the outer surface and the porosity were then measured. As a result, the surface roughness Ra of the outer surface was 18 μm and the porosity was 36%. Furthermore, the amount of metal impurities was investigated in the same manner as in Example 1. The amounts of metal impurities were 0.2 ppm for Fe, 0.2 ppm for Cr, 0.2 ppm for Ni, and 0.1 ppm for Cu. The results are shown in Table 2. Furthermore, similar to Example 1, we investigated the deformation of the quartz glass crucible, the shedding of powder, and whether the quartz glass crucible was deformed after use. The results are shown in Table 2.

[0058] (Comparative Example 5) A quartz glass crucible was manufactured under the same conditions as in Example 1, except that the outer surface of the quartz glass crucible was reacted with chlorine gas at 1200°C at a flow rate of 5 liters / min for 2 hours. The roughness of the outer surface and the porosity were then measured. As a result, the surface roughness Ra of the outer surface was 10 μm and the porosity was 23%. Furthermore, the amount of metal impurities was investigated in the same manner as in Example 1. The amounts of metal impurities were 0.8 ppm for Fe, 0.7 ppm for Cr, 0.7 ppm for Ni, and 0.6 ppm for Cu. The results are shown in Table 2. Furthermore, similar to Example 1, we investigated the deformation of the quartz glass crucible, the shedding of powder, and whether the quartz glass crucible was deformed after use. The results are shown in Table 2.

[0059] (Comparative Example 6) As shown in Table 1, quartz glass crucibles were manufactured under the same conditions as in Example 1, except that chlorine gas was reacted with the outer surface of the quartz glass crucible at 1200°C at a flow rate of 35 liters / min for 2 hours. The roughness of the outer surface and the porosity were then measured. As a result, the surface roughness Ra of the outer surface was 11 μm and the porosity was 24%. Furthermore, the amount of metal impurities was investigated in the same manner as in Example 1. The amounts of metal impurities were 0.6 ppm for Fe, 0.5 ppm for Cr, 0.5 ppm for Ni, and 0.5 ppm for Cu. The results are shown in Table 2.

[0060] Furthermore, similar to Example 1, we investigated the deformation of the quartz glass crucible, the shedding of powder, and whether the quartz glass crucible was deformed after use. The results are shown in Table 2.

[0061] [Table 1]

[0062] [Table 2]

[0063] Thus, when a reactive gas, mainly chlorine-based gas, is reacted with the outer surface of a quartz glass crucible, if the reaction temperature is below 1000°C, the roughness and porosity of the outer surface are large, and even if there are many opportunities for contact with the chlorine-based gas, the reaction is less likely to occur when the chlorine-based gas comes into contact with the outer surface layer, resulting in a lower effect on reducing metal impurities and thus a higher metal impurity content (Comparative Example 4). On the other hand, if the temperature is higher than 1300℃, there is a risk that the crucible will deform (Comparative Example 2).

[0064] Furthermore, if the flow rate of the reactive gas is less than 10 liters / min, the reaction does not proceed well because it does not easily reach the outer surface of the quartz glass crucible (Comparative Example 5), resulting in a low removal effect, which is undesirable. Furthermore, if the flow rate of the reactive gas exceeds 30 liters / min, the reactive gas is replaced by new gas and discharged before it can diffuse into the layer on the outer surface of the quartz glass crucible, which hinders the diffusion of the reaction and reduces the removal effect, making it undesirable (Comparative Example 6). Furthermore, when the reaction time was shorter than 1 hour (Comparative Example 3), and the surface roughness was coarse and the porosity was large, although the area in contact with the outer surface was wider, the reaction between the reactive gas and metal impurities did not proceed well to the depths. The reaction between the outer surface and the reactive gas occurred only at the very surface and did not reach a depth of 1 mm from the surface. As a result, the analyzed concentration of metal impurities was high and the removal effect was low.

[0065] Furthermore, it was confirmed that the surface roughness and porosity can be changed by varying the flow rate of the hydrofluoric acid solution and the etching time (washing time). Specifically, comparing Example 1 and Example 3, it was observed that a higher flow rate of hydrofluoric acid solution resulted in more contact between the silica glass crucible's outer surface and the hydrofluoric acid solution, leading to greater etching, a rougher surface, and an increased porosity. Comparing Example 1 and Comparative Example 3, a longer washing time increased the exposure time to the hydrofluoric acid solution, making the surface more susceptible to etching, resulting in a rougher surface and increased porosity. Furthermore, it was confirmed that when the surface roughness Ra of the outer surface is 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface is 20% or more and 30% or less, the content of each metal element contained in the outer surface of the quartz glass crucible is less than 0.5 ppm.

Claims

1. A method for manufacturing a quartz glass crucible for pulling silicon single crystals, wherein the content of each metal element contained in the outer surface of the quartz glass crucible is less than 0.5 ppm, the surface roughness Ra of the outer surface is 8 μm or more and 15 μm or less, and the porosity at a depth of 1 mm from the outer surface is 20% or more and 30% or less, After molding and melting quartz powder to form a quartz glass crucible, A method for producing a quartz glass crucible, characterized by including a step of reacting the outer surface of the quartz glass crucible with a reactive gas mainly composed of chlorine.

2. The method for producing a quartz glass crucible according to claim 1, characterized in that the step of reacting the outer surface of the quartz glass crucible with a reactive gas mainly composed of chlorine is performed in a temperature range of 1000°C to 1300°C.

3. After a process in which the outer surface of a quartz glass crucible is reacted with a reactive gas mainly composed of chlorine, The method for manufacturing a quartz glass crucible according to claim 1, characterized in that the outer surface of the quartz glass crucible is etched with an acid mainly composed of hydrofluoric acid.

Images